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2018 Sierra 1500 Denali - Battery Draining Overnight, P0622 Code

0

Nicole W. · rep 0 · May 22, 3:41 AM · 1 replies · solved · Question

Hey everyone,

I'm having a super frustrating issue with my 2018 GMC Sierra 1500 Denali. The battery keeps draining overnight, sometimes even after just a few hours. I replaced the battery about two months ago, thinking that was the problem, but it's still happening.

I managed to get a P0622 code (Generator F-Terminal Circuit) when I checked it with my OBD scanner. Could this be related to a parasitic draw, or is it something more serious with the alternator? It's really annoying to wake up to a dead truck, especially when I need it for work.

Any ideas on what I should check first? I've already made sure all the lights are off and nothing is obviously left plugged in.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:41 AM

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ClearTheCode guidance (Gmc · Electrical & electronics)

Summary: For 2018 Sierra 1500 Denali - Battery Draining Overnight, P0622 Code, work through these steps on your 2016+ vehicle:

  1. Confirm the symptom — note when it happens (cold start, highway, after fuel fill, etc.).
  2. Scan codes — save all pending/stored DTCs; don't clear until you've recorded them.
  3. Check TSBs & recalls — look up your VIN for open campaigns and known fixes.
  4. Inspect the obvious — related fuses, connectors, fluid level, and recent repairs.
  5. Test the common fix — follow model-specific service procedures; one change at a time.
  6. Escalate if needed — burning smell, no brakes, overheating, or stalling in traffic → shop visit.

Owner reported: Hey everyone,

I'm having a super frustrating issue with my 2018 GMC Sierra 1500 Denali. The battery keeps draining overnight, sometimes even after just a few hours. I replaced the battery about two months ago, thinking that was the problem, but it's still happening.

I managed to get a P0622 code (Generator F-Terminal Circuit) when I checked it with my OBD scanner. Could this be related to a para…

This is educational guidance, not a substitute for hands-on diagnosis.

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